The efficient utilization of HF is important from both economic and process operability viewpoints. Techniques to effect the separation and recovery of HF from fluorocarbon process streams have been disclosed.
U.S. Pat. No. 2,450,415 discloses the use of a continuous separation zone to separate an organic phase from HF and then recycling the latter to the reactor feed system.
U.S. Pat No. 3,406,099 discloses an azeotropic system useful for separation of CF.sub.3 COCF.sub.3, HF or CCl.sub.2 FCClF.sub.2 from mixtures containing one or more of these materials.
U.S. Pat. No. 3,873,629 discloses a continuous process for separating mixtures of HF and ClCHF.sub.2 by countercurrent contact of a gaseous mixture of the two components with H.sub.2 SO.sub.4.
U.S. Pat. No. 3,947,558 discloses a process for the separation of HF from the reaction products generated by fluorinating a 1-3 carbon chlorinated hydrocarbon by first separating HCl, followed by cooling to form an HF-rich layer and a substantially HCl-free organic layer. This latter layer is mixed with a liquid 2 to 8 carbon glycol; after which an HF enriched glycol layer is separated from the halocarbon layer. HF is recovered from the glycol by distillation.
U.S. Pat. No. 3,976,447 discloses the separation of HF from gaseous mixtures by treatment with dry particles of CaCl.sub.2, BaCl.sub.2, or SrCl.sub.2, after which the HF is desorbed.
U.S. Pat. No. 4,209,470 discloses a process for the separation of HF from its liquid mixtures with 1-chloro-1,1-difluoroethane by adding an auxiliary solvent to enhance the HF composition of a liquid inorganic phase in a decanter. The HF is then separated from the inorganic phase by distillation.
EP 98,341 discloses a process for the separation of HF and 1-chloro-1,1-difluoroethane which does not require an auxiliary solvent even though the feed stream to the decanter contains pentafluorobutane which the disclosure states should contribute to the mutual solubility of HF and 1-chloro-1,1-difluoroethane; and therefore, should hinder a phase separation process. The separation is done without the use of auxiliary solvents by avoiding contamination and exercising good temperature control.
The need to produce alternate fluorocarbons useful as refrigerants and blowing agents or as intermediates in the production of other fluorocarbons useful as refrigerants and blowing agents has spurred an interest in processes for the preparation of FC-123 and FC-124. These are useful themselves as blowing agents, refrigerants and intermediates in the preparation of 1,1,1,2-tetrafluoroethane (FC-134a), a highly useful fluorocarbon refrigerant.
One process for the preparation of FC-123 and FC-124, described in commonly assigned application Ser. No. 070,826, filed July 7, 1987,now U.S. Pat. No. 4,766,260 involves vapor phase hydrofluorination of halogenated alkenes with excess HF. This process produces a reaction mixture effluent consisting essentially of HF, FC-123, FC-124, tetrachloroethylene, HCl, and minor (less than 5 mole percent) amounts of other halogenated products such as 1,2,2-trichloro-1,1-difluoroethane (FC-122) and pentafluoroethane (FC-125). To maximize process efficiency it is desirable to recycle HF, FC-122, tetrachloroethylene, and a portion of the FC-123 to the synthesis reactor. It is particularly desirable to separate excess HF from the organic components of the reaction mixture effluent. This invention provides for a mechanism to accomplish this by controlling the ratio of HF/FC-123 in the mixture followed by azeotropic distillation.